1. Field of the Invention
The invention relates to a method for forming a sealed coupling between two bodies, and more particularly to a method for releasably sealing a pipe to a body through which the pipe penetrates. The invention is particularly useful in a nuclear reactor for sealing the thermocouple columns with respect to the nuclear reactor closure head which is penetrated by the thermocouple columns.
2. Description of the Prior Art
In a nuclear reactor, such as a pressurized water nuclear reactor, the closure head of the reactor vessel is penetrated by a plurality of thermocouple columns. Various electrical leads and control mechanisms pass through the thermocouple columns from the exterior of the vessel to the interior of the vessel where they are connected with control apparatus within the vessel. Because the reactor vessel is pressurized during operation, it is necessary that the penetrations of the thermocouple columns through the closure head be sealed in order to prevent any leakage through these penetrations. Further, because the reactor closure head is periodically removed during the life of the reactor, for example for refueling and other service operations, the seal between each thermocouple column and its penetration cannot be permanent; rather such seal must be capable of being released and re-formed relatively quickly so as not to impede the removal and replacement of the reactor closure head.
In a known method of sealing a thermocouple column with respect to the reactor closure head, a female flange is permanently welded to the structure forming the vessel head penetration for each thermocouple column. The end of the female flange remote from the closure head is provided with a shoulder having an abutment surface. The thermocouple column passes through the closure head penetration as well as the associated female flange. A male flange, through which the thermocouple column also passes, is likewise provided with a shoulder which has an abutment surface in mating relationship in the axial direction with the abutment surface of the female flange. A metal deformable gasket is placed between the mating abutment surfaces. The shoulders of the male and female flanges present an outer contour having a frustro-conical section. A segmented yoke having an inner circumferential recess with a frustro-conical section fits about the shoulders of the mating flanges and is provided with tangentially oriented bolts which when tightened cause the yoke to pinch together the shoulders and hence the adjacent abutment surfaces of the male and female flanges, compressing the gasket and forming a metal to metal seal between the male and female flanges.
A similar seal is formed between an abutment surface provided on the outer surface of the thermocouple column and an adjacent abutment surface provided at the other end of the male flange. In this latter seal, however, the abutment surfaces are brought together to compress the metal gasket by an axial force which is provided by axially oriented bolts which are arranged to compress the adjacent abutment surfaces together as the bolts are tightened.
The seals formed by the foregoing method, like other mechanical seals, deteriorate over a period of time and begin leaking. Leakage through the seals formed by the foregoing method can be temporarily stopped by further tightening the tangentially oriented bolts around the segmented yoke in the case of the seal between the male and female flanges, and further tightening the axially oriented bolts in the case of the seal between the thermocouple column and the male flange.